The present invention relates in general to bonding pads and, more particularly, to a bonding pad having a circular exposed area.
An integrated circuit typically contains metal channels for routing signals throughout the IC. To interconnect the IC circuitry to the outside world, most if not all ICs use bonding pads to connect the metal channels through bonding wires to the pins of the IC package. The bonding pad is disposed on top of the semiconductor substrate. The bonding pad is typically composed of aluminum with small portions of copper and/or silicon. A passivation layer comprising a glass material such as silicon oxide or nitride insulates the substrate and bonding pads from contamination, corrosion and other external environmental conditions. In the prior art, a square or rectangular portion of the passivation layer material is etched out exposing the bonding pad to make a point of contact for the bonding wire to adhere.
A common problem associated with bonding pads occurs in high voltage ICs. The high voltage ICs typically have high voltage bonding pads and associated metal channels, and low voltage metal channels. Although the passivation layer is by nature an insulator, it is possible to induce a sufficient potential across the passivation layer to breach through its dielectric and short the low voltage metal channel. The electric field formed by application of a high voltage, say 400 volts or more, to the high voltage bonding wire could cause a punch through of the passivation layer from the high voltage bonding pad to the low voltage metal channel thereby damaging the IC.
The problem has long been attributed to sharp perimeter corners of the rectangular bonding pad. Prior art solutions have involved increasing the distance between the high voltage bonding pad and the low voltage metal channel, or providing some type of protection circuitry, e.g. diode protection, between the high voltage bonding pad and the low voltage metal channel. Yet punch through problems continue to plague many high voltage ICs.